Highly Stable Three Lithium Insertion in Thin V 2 O 5 Shells on Vertically Aligned Carbon Nanofiber Arrays for Ultrahigh‐Capacity Lithium Ion Battery Cathodes

Here the authors demonstrate an approach to achieving stable 3 Li + insertion into vanadium pentoxide (V 2 O 5 ) by implementing a 3D core–shell structure consisting of coaxial V 2 O 5 shells sputter‐coated on vertically aligned carbon nanofiber cores. The hydrated amorphous microporous structure in the “as‐deposited” V 2 O 5 shells and the particulated nanocrystalline V 2 O 5 structure formed by thermal annealing are compared. The former provides remarkably high capacities of 360 and 547 mAh g −1 in the voltage range of 4.0–2.0 and 4.0–1.5 V, respectively, far exceeding values in current oxide‐based lithium ion battery cathodes and even the corresponding theoretical values of 294 mAh g −1 for 2 Li + /V 2 O 5 insertion and 441 mAh g −1 for 3 Li + /V 2 O 5 insertion into crystalline V 2 O 5 materials. This is attributed to the additional reactions with the hydrated amorphous structure. After 100 cycles of 3 Li + /V 2 O 5 insertion/extraction at 0.20 A g −1 (≈ C /3), ≈84% of the initial capacity is retained. After thermal annealing, the core–shell structure presents a capacity of 294 and 390 mAh g −1 , matching well with the theoretical values for 2 and 3 Li + /V 2 O 5 insertion. The annealed sample shows further improved stability, with a remarkable capacity retention of ≈100% and ≈88% for 100 cycles of 2 and 3 Li + /V 2 O 5 insertion/extraction.